Reset OpenGL lights?
You can find the defaults by opening a new instance of blender and loading the defaults (without saving the default.blend) and using python to get the default values:

import bpy

for light in bpy.context.user_preferences.system.solid_lights:
    print(light.direction)


Which will print:

&lt;Vector (-0.8920, 0.3000, 0.9000)&gt;
&lt;Vector (0.5880, 0.4600, 0.2480)&gt;
&lt;Vector (0.2160, -0.3920, -0.2160)&gt;


So to set the light directions to the defaults, run:

import bpy

bpy.context.user_preferences.system.solid_lights[0].direction = (-0.892, 0.3, 0.9)
bpy.context.user_preferences.system.solid_lights[1].direction = (0.5880, 0.4600, 0.2480)
bpy.context.user_preferences.system.solid_lights[2].direction = (0.2160, -0.3920, -0.2160)